The present invention relates to a distraction device for moving a one-piece or two-piece or separated bone apart in order to extend or bridge a bone gap, optionally in the form of an intramedullary nail which can be inserted into a medullary space of a bone and has at least two elements which can be moved axially in relation to one another, the first element being connected to the second element via at least one detent device for securing a distraction movement.
Distraction devices of this kind are known and commercially available in a wide variety of designs. They are used primarily to ensure that, when a bone has been cut through, suitable distraction takes place in order to improve endogenous formation of new bone substance. A corresponding distraction device is described in EP 0 346 247 B1, for example, in which an intracorporeal bone intramedullary nail is disclosed which moves two parts of a bone by mechanical means. Such a distraction device is not suitable for very small bones with small cross sections. Moreover, DE 39 21 972 C2 discloses an intramedullary nail which can likewise be lengthened by mechanical means. A disadvantage of the distraction devices known in the prior art is that they are much too large and their degree of efficiency is poor. They can transmit distraction forces to bones only to a limited extent.
A further disadvantage is that distraction devices with a small cross section and with high distraction forces have hitherto been impossible to produce.
EP 0 919 717 A1 describes a drive device with an element made of a shape-memory alloy, and the use thereof. In said document, two pusher modules are moved toward one another, with distraction taking place purely through the compression forces of the shape-memory alloy.
A similar principle is described in the Journal of Physics D. applied physics IOP Publishing, Bristol, GB, volume No. 29, No. 3, of Mar. 14, 1996, pages 923 through 928, in the article entitled “Electromagnetic heating of a shape memory alloy translator”. There, a distraction between two pusher modules leads to distraction of a piston, likewise through the action of compression forces generated by a shape-memory alloy.
WO 00/01315 A discloses a distraction device in which, in an actuating device, tensile forces are generated which directly transmit a distraction to a piston via a pusher element 5.
Therefore, it is an object of the present invention to make available a distraction device of the type mentioned at the outset, which avoids the stated disadvantages and with which high distraction forces can be achieved with extremely small external diameters.